Light dark matter from the U(1)_X sector in the NMSSM with gauge mediation

Cosmic ray anomalies observed by PAMELA and Fermi-LAT experiments may be interpreted by heavy (TeV-scale) dark matter annihilation enhanced by Sommerfeld effects mediated by a very light (sub-GeV) U(1)_X gauge boson, while the recent direct searches from CoGeNT and DAMA/LIBRA experiments may indicate a rather light ( ∼ 7 GeV) dark matter with weak interaction. Motivated by these apparently different scales, we consider a gauge mediated next-to-the minimal supersymmetric standard model (NMSSM) entended with a light U(1)_X sector plus a heavy sector (_h,H_h), which can provide both a light ( ∼ 7 GeV) and a heavy (TeV-scale) dark matter without introducing any ad hoc new scale. Through the Yukawa coupling between H_h and the messager fields, the U(1)_X gauge symmetry is broken around the GeV scale radiatively and a large negative m_S² is generated for the NMSSM singlet S. Furthermore, the small kinetic mixing parameter between U(1)_X and U(1)_Y is predicted to be θ ∼ 10⁻⁵−10⁻⁶ after integrating out the messengers. Such a light dark matter, which can have a normal relic density from the late decay of the right-handed sneutrino (assumed to be the ordinary next-to-the lightest supersymmetric particle and thermally produced in the early Universe), can serve a good candidate to explain the recent CoGeNT and DAMA/LIBRA results.